JP2010238534A - Membrane-electrode assembly for fuel cell, and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane-electrode assembly for a fuel cell, having improved drainage and gas distributing performance, resulting in no occurrence of flooding. <P>SOLUTION: The membrane-electrode assembly for the fuel cell includes a solid electrolyte membrane on each side of which an electrode catalyst layer, a porous base layer 3, and a porous diffusion layer 4 having coarser pores than the base layer 3 are laminated in sequence. On the base layer 3 and the diffusion layer 4, water repellent portions 3a, 4a and hydrophilic portions 3b, 4b are formed separating each other in their interlayer directions. The water repellent portions 3a, 4a and the hydrophilic portions 3b, 4b range over the base layer 3 and the diffusion layer 4. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fuel cell membrane electrode assembly and a method for producing the same, and more particularly to an improvement in a structure in which an intermediate layer is provided between an electrode catalyst layer and a diffusion layer.

A fuel cell is configured by laminating separators on both sides of a flat membrane electrode assembly. The membrane electrode assembly has a polymer electrolyte membrane between a positive electrode catalyst layer and a negative electrode catalyst layer. It is a laminate in which a gas diffusion layer is laminated on the outside of each electrode catalyst layer. According to such a fuel cell, for example, when hydrogen gas is caused to flow through the gas passage of the separator disposed on the negative electrode side and an oxidizing gas is caused to flow through the gas passage of the separator disposed on the positive electrode side, an electrochemical reaction occurs. Electric current is generated. During operation of the fuel cell, the gas diffusion layer transmits electrons generated by the electrochemical reaction between the electrode catalyst layer and the separator, and simultaneously diffuses the fuel gas and the oxidizing gas. The electrode catalyst layer on the negative electrode side causes a chemical reaction to the fuel gas to generate protons (H ⁺ ) and electrons, the electrode catalyst layer on the positive electrode side generates water from oxygen, protons and electrons, and the electrolyte membrane is a proton. Is ion-conducted. Then, electric power is taken out through the positive and negative electrode catalyst layers.

  The generated water is discharged to the outside through the diffusion layer, but if drainage is not performed well, water accumulates in the pores of the diffusion layer, causing a phenomenon called flooding that inhibits the supply of fuel gas and air . Therefore, in the diffusion layer, it is indispensable to improve the performance of the fuel cell that water is drained well.

In order to solve the above problems, for example, in Patent Document 1, a microporous layer (underlayer) formed by mixing carbon particles and a water repellent agent is formed between a gas diffusion layer and an electrode catalyst layer. It is described. The role of the microporous layer is to facilitate the movement of the fuel gas and the oxidant gas to the anode side gas diffusion electrode and the cathode side gas diffusion electrode, or the water generated at the cathode side gas diffusion electrode during the electrode reaction It is easy to discharge into the gas distribution groove.
Further, Patent Document 2 discloses that a water-repellent treated carbon particle and a hydrophilic treated carbon particle are formed as a microporous layer (water-repellent layer) between a gas diffusion layer and an electrode catalyst layer. What was comprised so that it might continue in the thickness direction was disclosed. Thereby, a water permeation path is provided in a part of the water repellent layer to improve drainage.
Patent Document 3 also describes a product in which highly water-repellent portions are distributed in the plane of the gas diffusion layer for the purpose of improving drainage and the like.

JP 2004-172095 A JP 2006-179317 A JP 2003-132898 A

  However, in the technique described in Patent Document 2, since the water-repellent layer is formed by mixing the water-repellent carbon particles and the hydrophilic carbon particles, the same type of carbon particles are efficiently removed continuously in the thickness direction. It is difficult to line up. Furthermore, even if the techniques described in Patent Document 2 and Patent Document 3 are combined, the water-repellent layer and the gas diffusion layer are created separately. It is difficult to sufficiently communicate with the road, and drainage and gas flow are insufficient.

  In view of the above-described problems, the present invention can improve drainage and gas flowability by providing a continuous water-repellent part and a hydrophilic part in the base layer and the diffusion layer, and can simplify such a configuration. It aims at providing the membrane electrode composite for fuel cells which can be manufactured, and its manufacturing method.

  The membrane electrode assembly for a fuel cell of the present invention comprises an electrode layer, a porous underlayer, and a porous diffusion layer having pores coarser than the underlayer in this order on both surfaces of a solid electrolyte membrane. A membrane electrode assembly for a fuel cell, wherein a water repellent part and a hydrophilic part are formed separately from each other in the interlayer direction in the base layer and the diffusion layer, The hydrophilic portion is characterized by being continuous over the base layer and the diffusion layer.

  Further, in the method for producing a membrane electrode assembly for a fuel cell of the present invention, a first base paste containing a water repellent component is applied to a part of one surface of the diffusion layer constituting member, and one surface of the diffusion layer constituting member And applying a second base paste containing a hydrophilic component to a portion where the first base paste is not applied, and allowing the water repellent component and the hydrophilic component to penetrate into the diffusion layer constituting member; A step of drying the diffusion layer constituting member to which the first and second base pastes are applied is provided.

  In the fuel cell membrane electrode assembly, since the water repellent part and the hydrophilic part are continuous over the base layer and the diffusion layer, water flows through the hydrophilic part over the base layer and the diffusion layer, Gas flows through the water-repellent part over the base layer and the diffusion layer. Thus, in this invention, since the flow path of water and gas is not interrupted | blocked between a base layer and a diffusion layer, they can be distribute | circulated smoothly.

  In the method for producing a membrane electrode assembly for a fuel cell according to the present invention, the water-repellent first base paste and the hydrophilic second base paste are applied and penetrated on one surface of the diffusion layer constituting member. The water repellent part and the hydrophilic part can be formed on the diffusion layer constituting member simultaneously with the formation of the base layer. Therefore, a structure in which the water repellent part and the hydrophilic part are continuous with the base layer and the diffusion layer can be formed by a simple process.

  According to the present invention, since the water-repellent part and the hydrophilic part are continuous in the base layer and the diffusion layer, it is possible to obtain good drainage properties and gas flowability, and to prevent flooding from occurring. . Further, according to the present invention, it is possible to easily manufacture a configuration in which the water repellent part and the hydrophilic part are continuous in the underlayer and the diffusion layer.

It is sectional drawing which shows the membrane electrode assembly of one Embodiment of this invention. It is sectional drawing which shows the manufacturing process of the membrane electrode assembly of one Embodiment of this invention. It is a photograph of the membrane electrode assembly manufactured in the Example of this invention.

  An embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a cross-sectional view showing a membrane electrode assembly A of the embodiment. In this membrane electrode assembly A, a positive electrode catalyst layer 2a and a negative electrode catalyst layer 2b are laminated on both surfaces of the solid electrolyte membrane 1, and a base layer 3 is formed outside each of the electrode catalyst layers 2a and 2b. In addition to being laminated, the diffusion layer 4 is laminated outside the base layer 3.

  The laminated structure of the polymer electrolyte membrane 1 and the electrode catalyst layers 2a and 2b is prepared, for example, by applying and drying a catalyst paste in which a catalyst is dispersed on a sheet to produce an electrode sheet. It is configured by transferring onto the surface of the film 1. The diffusion layer 4 is made of, for example, porous carbon paper, and the underlayer 3 is made of carbon material such as graphite, acetylene black, or vapor grown carbon fiber, and polytetrafluoroethylene (PTFE), fluorinated ethylene. A water repellent component such as propylene copolymer (FEP) or polyvinylidene fluoride (PVDF) is mixed.

  Next, with reference to FIG. 2, a procedure for forming a laminated structure of the diffusion layer 4 and the underlayer 3 will be described. First, a mask is provided on one surface of the diffusion layer 4. As this mask, for example, a mask in which mask portions are intermittently formed in a lattice shape can be used. Next, a water repellent paste is applied from above the mask with, for example, a brush or a roller. This water repellent paste contains a water repellent component.

  When the water repellent paste is applied to the diffusion layer 4, the water repellent component contained in the water repellent paste soaks into the diffusion layer 4 as shown in FIG. The soaked water-repellent component is allowed to stand until it reaches the back surface of the diffusion layer 4 and then dried. Next, the mask is peeled off from the diffusion layer 4 and another mask is provided on the diffusion layer 4 to cover the portion where the water-repellent paste is applied.

  Next, a hydrophilic paste is applied over the mask. This hydrophilic paste contains a hydrophilic component. When the hydrophilic paste is applied to the diffusion layer 4, the hydrophilic component contained in the hydrophilic paste soaks into the diffusion layer 4 as shown in FIG. Then, the soaked hydrophilic component is left until it reaches the back surface of the diffusion layer 4 and then dried. Next, the mask is peeled off from the diffusion layer 4 and the diffusion layer 4 is baked. In this way, a laminated structure of the diffusion layer 4 and the underlayer 3 is configured. Instead of using a mask as described above, for example, a water-repellent paste and a hydrophilic paste can be sequentially applied by a screen printing method.

  In the laminated structure of the diffusion layer 4 and the base layer 3 configured as described above, the water-repellent portions 3a and the hydrophilic portions 3b of the base layer 3 are arranged in a lattice shape in plan view. On the other hand, in a cross-sectional view, as shown in FIG. 2C, the water-repellent part 3a of the base layer 3 and the water-repellent part 4a of the diffusion layer 4 in which the water-repellent component is immersed are continuous, The portion 3b and the hydrophilic portion 4b of the diffusion layer 4 in which the hydrophilic component is immersed are continuous. The underlayer 3 is laminated so as to be in contact with the electrode catalyst layers 2a and 2b, whereby the membrane electrode assembly A is configured. The underlayer 3 is a porous body with finer pores than the diffusion layer 4, and the fuel gas and air flowing from the diffusion layer 4 are made uniform and sent to the electrode catalyst layers 2a and 2b.

A separator is laminated on both sides of the membrane electrode assembly A having the above structure to constitute a fuel cell. In such a fuel cell, the electrode catalyst layer 2b on the negative electrode side causes a chemical reaction to the fuel gas to generate protons (H ⁺ ) and electrons, and the electrode catalyst layer 2a on the positive electrode side generates water from oxygen, protons and electrons. And the electrolyte membrane conducts protons to the electrode catalyst layer 2a on the positive electrode side. And electric power is taken out through the positive and negative electrode catalyst layers 2a and 2b.

  Here, FIG. 2C shows a laminated structure of the diffusion layer 4 and the base layer 3 on the positive electrode side. The water produced in the electrode catalyst layer 2a on the positive electrode side is discharged to the separator through the base layer 3 and the hydrophilic portions 3b and 4b of the diffusion layer 4. Further, the fuel gas is supplied from the separator to the electrode catalyst layer 2a on the positive electrode side through the base layer 3 and the water repellent portions 3a, 4a of the diffusion layer 4. In this case, since the water repellent parts 3 a and 4 a and the hydrophilic parts 3 b and 4 b are continuous with the base layer 3 and the diffusion layer 4, water flows through the hydrophilic parts 3 b and 4 b across the base layer 3 and the diffusion layer 4. Then, the fuel gas flows through the water repellent portions 3 a and 4 a across the base layer 3 and the diffusion layer 4. Therefore, since the flow path of water and fuel gas is not blocked between the base layer 3 and the diffusion layer 4, water and fuel gas can be smoothly circulated and flooding can be prevented from occurring. Can do.

  Moreover, in the manufacturing method of the membrane electrode assembly for a fuel cell described above, since the water repellent part 4a and the hydrophilic part 4b can be formed on the diffusion layer 4 simultaneously with the formation of the base layer 3, the water repellent part A configuration in which 3a, 4a and hydrophilic portions 3b, 4b are continuous with the underlayer 3 and the diffusion layer 4 can be formed by a simple process.

Next, the present invention will be described in more detail with reference to examples.
A dispersion in which FEP (water repellent component) was dispersed in water and ethylene glycol were mixed to prepare an FEP solution. 5 parts by weight of vapor grown carbon fiber (VGCF) was added to 100 parts by weight of this solution and stirred and kneaded to prepare a water-repellent paste.

  In addition, an electrolyte solution was prepared by dissolving a polymer electrolyte (Nafion, hydrophilic component, manufactured by DuPont) in N-methylpyrrolidone (NMP), and 5 parts by weight of a carbon material obtained by mixing 100 parts by weight of this solution with ketjen black and VGCF. Part was added and kneaded to prepare a hydrophilic paste.

  The water-repellent paste and the hydrophilic paste were applied to a 5 mm square lattice pattern on carbon paper by screen printing. The carbon paper was immersed in the water-repellent component of the water-repellent paste and the hydrophilic component of the hydrophilic paste by leaving for 30 minutes. Thereafter, the carbon paper was dried and fired to obtain a laminated structure of an underlayer and a diffusion layer.

  When the laminated structure of the base layer and the diffusion layer was immersed in water with the diffusion layer facing down, water balls were formed in the portion where the hydrophilic paste was applied, as shown in FIG. This indicates that the hydrophilic component has penetrated to the back surface of the carbon paper.

  In each of the above examples, each paste is formed in a 5 mm square grid, but one side of the grid is preferably 1 to 5 mm. Moreover, it can also be set as another form not only in a grid | lattice form. For example, the part of the gas diffusion layer facing the gas passage of the separator can be made water-repellent and the other part can be made hydrophilic.

  Since the present invention can prevent the occurrence of flooding by smoothly flowing water and fuel gas, it is extremely promising when applied to an automotive fuel cell that requires high reliability.

1 Solid electrolyte membrane 2a, 2b Electrocatalyst layer (electrode layer)
3 Underlayer 4 Diffusion layer

Claims (2)

  A fuel cell membrane electrode composite comprising, on both sides of a solid electrolyte membrane, an electrode layer, a porous underlayer, and a porous diffusion layer having pores coarser than the underlayer in this order, In the base layer and the diffusion layer, a water repellent part and a hydrophilic part are formed separately from each other in the direction of the interlayer, and the water repellent part and the hydrophilic part are formed on the base layer and the diffusion layer. A membrane electrode assembly for a fuel cell, characterized in that the membrane electrode assembly is continuous. A first base paste containing a water repellent component is applied to a part of one surface of the diffusion layer constituting member, and a hydrophilic portion is applied to a part of the surface of the diffusion layer constituting member that is not coated with the first base paste. Applying a second base paste containing a sexual component and allowing the water repellent component and the hydrophilic component to penetrate into the diffusion layer constituting member;
A method of producing a membrane electrode assembly for a fuel cell, comprising the step of drying the diffusion layer constituting member to which the first and second base pastes are applied.

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